The mass spectrometric analysis of the major chain d1, one of the four heme-binding chains in earthworm hemeglobin of Lumbricus terrestris, revealed a difference between the measured and the sequence derived masses indicated errors in the resported sequence. The purpose of this study is to clarify the possible sequence ambiguity by mass spectrometric peptide mapping experiments. After the digestion of chain d with a number of enzymes, proteolytic peptides in the region of 51-140 were identified and indicated a correct sequence assignment in this region. In addition, digestin withV8 protease revealed an sequence error in position 58 (E instead of Q). N-terminal Edman sequencing allowed the correction of misidentified amino acids 7 (G7S), 23 (Q23E) and 33 (K33R). The refined sequence (1-140) results in a molecular mass of resolution of these resolution of these discrepancies has been published Q, Zie, R.A. Donahue Jr., K. Schneider, U.A. Mirza, I. Haller, B.T. C hait & A.F . Riggs "Structure of chain d of the gigantic hemoglobin of the earthworm" BBA 1337, (1997) 241-247.